Pill Interference

Women who take birth control pills should avoid Saint-John's-wort—or use backup contraception. In an Indiana University study, 7 of 12 Pill users experienced breakthrough bleeding—a sign of reduced Pill effectiveness— after taking the herbal supplement for two months. Saint-John's-wort boosts a liver enzyme, speeding up the Pill's removal from the body, says pharmacology professor Chris Gorski. The risk of Pill failure may differ by the source and dose of the herb, but he says the combination has been linked to several pregnancies. Saint-John's-wort may also alter the body's response to other drugs, Gorski adds.